Move idle detection classes to its own directory

Reviewed By: AaaChiuuu

Differential Revision: D4738755

fbshipit-source-id: df3b215991a45932283f6ba9d800aeff1c31d2e6

ReactAndroid/src/androidTest/java/com/facebook/react/testing/ReactAppInstrumentationTestCase.java

@@ -20,6 +20,7 @@ import android.view.ViewGroup;
 
 import com.facebook.infer.annotation.Assertions;
 import com.facebook.react.bridge.ReactContext;
+import com.facebook.react.testing.idledetection.IdleWaiter;
 
 /**
  * Base class for instrumentation tests that runs React based react application in UI mode
@@ -123,7 +124,6 @@ public abstract class ReactAppInstrumentationTestCase extends
       }
     };
 
-
     getActivity().runOnUiThread(getScreenshotRunnable);
     try {
       if (!latch.await(5000, TimeUnit.MILLISECONDS)) {